1. Field of the Invention
This invention relates to electrolytic cells having plane (flat or curved) electrodes in a liquid electrolyte and to the electro-chemical treatment of waste effluents or other solutions using such electrolytic cells.
2. Prior Art
In electrolytic cells using liquid electrolytes, the maximum current density is usually limited by the ionic depletion of the electrolyte immediately adjacent the surface of the electrode on which material is deposited. This problem arises very particularly with cells for electro-chemical reactions involving very dilute or low concentration electrolytes, such as are used for example in the recovery of metals and in the electrochemical treatment of dilute toxic solutions. In the layer of electrolyte immediately adjacent the cathode surface of a cell in which a metal is being deposited on the cathode, the limit to the current density arises because the rate of deposition of metal cannot be greater than the rate of diffusion of the metal ions into the layer of solution adjacent the electrode. If any attempt is made to pass a greater current through the cell, this will result in the evolution of hydrogen (assuming the electrolyte is an aqueous solution).
In attempts to overcome this problem, it has been proposed to use a fast flow of electrolyte through the cell to break up the boundary layer. Another way proposed is the use of rotating electrodes. Also it has been proposed to form an electrode, usually the cathode, as a fluidised bed of conducting material.
It is an object of the present invention to provide means for increasing the limiting current density in a cell having stationary electrodes.